Choosing a Flat Roof for Your Extension
A flat roof is the natural choice for most single-storey extensions, kitchen-diners and rear additions in Doncaster. It’s neat, it keeps sightlines low so it doesn’t tower over the garden, and it lets you add rooflights for plenty of natural light. If you’re planning an extension, here’s what to think about, and why the covering you choose matters more than anything.
Why flat roofs suit extensions
A flat roof keeps the extension low and unobtrusive, which often matters for both looks and planning. It also gives you a clean ceiling line inside and the option of glazing overhead. The key is choosing a covering that will last as long as the rest of the build, because re-roofing an extension a decade later is a job nobody wants.
Choose the right covering, and avoid the wrong one
This is where it pays not to cut corners. The covering decides whether your new roof is a problem you’ve solved or one you’ve postponed:
- Felt is cheap but short-lived, and its laps are the first thing to fail.
- EPDM rubber relies on adhesive seams and bonded details that age and let go, usually at the joints.
- GRP fibreglass is rigid, so it can craze and crack as the deck flexes, and it needs dry, warm weather to cure properly.
- Single ply membrane is welded into one continuous, joint-free skin, stays flexible, and carries a long manufacturer guarantee.
We’d recommend a welded single ply membrane every time. It’s the same reliability used on commercial buildings, on a domestic scale. For the full comparison, see EPDM vs GRP vs single ply.
Get the insulation and regulations right
A new extension roof has to meet current Building Regulations for thermal performance. In practice that means a warm-roof build-up, with the insulation above the deck and the membrane over the top. This keeps the room comfortable and avoids condensation problems down the line. Our guides to warm roof vs cold roof and building regulations explain this in more detail.
Don’t forget the details
- Rooflights and lanterns. Single ply dresses neatly around a rooflight kerb, so you can flood the room with light and stay watertight.
- Drainage. Proper falls to the outlets keep water clearing off the roof rather than ponding.
- Upstands and abutments. Where the new roof meets the existing house wall, good detailing is what keeps it dry for the long term.
Extension roofs across Doncaster and South Yorkshire
We fit extension roofs as part of our domestic flat roofing work throughout Doncaster, Rotherham, Barnsley and out to the likes of Bawtry and Tickhill, and we’re happy to advise at the planning stage. See everywhere we cover on our areas page.
Planning an extension? Get a free quote or call us on 07973 436 305.
Frequently asked questions
What is the best flat roof covering for an extension?
For most extensions we recommend a welded single ply membrane. It forms one continuous, joint-free skin with a long manufacturer guarantee, and it dresses neatly around rooflights. It avoids the short life of felt, the adhesive joints of EPDM and the cracking that rigid GRP can suffer.
Does an extension flat roof need to meet Building Regulations?
Yes. A new extension roof must meet current Building Regulations for thermal performance, which in practice means a warm-roof build-up with insulation above the deck and the membrane welded over the top. We design every extension roof to comply.
Can I have a rooflight or lantern in a single ply extension roof?
Yes. Single ply stays flexible, so it dresses neatly around a rooflight or lantern kerb and welds into a watertight detail. It is one of the best ways to flood a new room with natural light while staying fully sealed.
Do you build extension flat roofs in Doncaster?
Yes. We fit extension and kitchen-diner flat roofs across Doncaster, Rotherham, Barnsley, Bawtry, Tickhill and the surrounding South Yorkshire area, and we are happy to advise at the planning stage rather than just turning up to lay a roof.